That cube is two in one - nest area and outside world. It's good for a while but when colony gets bigger, You'll have to replace it or damage it (vinyl tubing). By flat housing I assume You mean those nest from acrylic, grout or ytong attached with tubes to outworlds. This option is easier to expand but takes more space. You don't need a very large outworld for ant colony because most of the ants will stay in nest area, so the only thing You need to expand is nest area. There are some great ideas on it, search on Youtube and Google :)

Now I get it, thank You for giving further information. Now in this case I would definitely stick with that "sandless cube". In that cube there's a hard material like gypsum or grout - easy to supply the nest with water. Now the simple sand housing like the one You mentioned above has a big flaw - SAND. You will need to spray the sand with water every one or two days to keep it moisturized. Ants will make tunnels in that sand and if it dries out, whole nest will collapse and might kill Your ants and the queen. So with this one You will have to be careful and take a good care of it. Hope this helps.

Thank you for this advice. My son is only 4 but very careful with things. His brotehr on the other hand is 3 and a tank. He will surely tap the glass when I am not looking. So if the nest collapses it will kill the colony. I also want to be able to leave the house for the weekend without having to ask someone to 'water the ants'. Now only choose if I go for the small 4 room cube, or fir the bigger 7 rooms one.

Dear Rozema,Cube size depends on Your colony size. If it is a small colony - go for the 4 room cube. Ants love tight spaces. If ants will have too much space, they will dump their litter in rooms which they won't use, that's gonna get mold - You will need to clean it every few days. Also mold has a small chance of getting diseases which can kill Your colony. Keep it small, You will notice when ants will need more space.Hope this helps :)